In an installation of this type, an analyzed document whose contents are transmitted to the reproduction unit is restored by a printing head or bar which scans a chosen sensitive paper along successive lines. The printing head or bar is energized by a data signal received by the reproduction unit and which defines the contents of the scanned line for printing the successive image dots along the scan line in question.
Image dots, and hence dots of variable density, are formed by causing, by reaction, a localized modification of the paper used so as to obtain a variation of its optical appearance, for example colouring. The paper used at the receiving unit can therefore be e.g. electro-sensitive, electro-catalytic or thermo-sensitive. Since the paper used is, for example, electro-catalytic, an image dot is printed by localized application on the paper of a stylus made of catalytic material chosen as a function of the paper and by passing an electric current between the stylus and the paper; catalysis accompanied by a change in the colour of the paper is thus caused. In this example, the paper can be constituted by an external layer of sensitive material, a conductive sub-layer and a base paper which supports them. The stylus can for example be made of or covered with silver; it presses against the external layer.
A complete image line can be printed by moving a single stylus printing head along a scan line of paper. A complete scan line can also be obtained by a printing bar which has as many printing styli as there are image dots to the line. The printing bar is static in relation to the scan line in question; there will be only a relative step by step movement between the paper and the printing bar. Such a bar may be constituted by a stack of conductive plates which are insulated from each other and each having an end which forms one of the styli.
The present invention aims to constitute a printing bar with a plurality of styli so equipped as to allow each of the styli to be controlled being easy to produce industrially.